This invention relates to the preparation of aluminum arsenide type semiconductor material and, more particularly to a method for the preparation of stable crystals of aluminum gallium arsenide compositions.
Aluminum arsenide is a III-V compound semiconductor and is an advantageous material for the manufacture of optoelectronic devices, such as light emitting diodes. Similar compounds such as gallium arsenide, gallium phosphide, or gallium arsenide phosphide, are widely used in such manufacture, but the application of aluminum arsenide has been limited. The limitations in the application of aluminum arsenide are caused by difficulties in the preparation of high-purity single crystals, the reactivity of aluminum and the instability of crystals when exposed to moisture, such as, for example, contained in ambient air.
Aluminum arsenide can be prepared using well known methods, such as liquid and vapor-phase epitaxy techniques or melt-growth techniques. However, aluminum arsenide crystals prepared by these methods are generally unstable and generate arsine when exposed to moist air.
It is known that the binary compound gallium arsenide is chemically stable, while mixtures of gallium arsenide and aluminum arsenide, which form pseudo-binary or ternary compounds of aluminum, gallium and arsenic, are stable only at certain levels of their aluminum arsenide content. Thus, it has been reported that aluminum arsenide may be chemically stabilized by substituting gallium for 30 to 40 % of the aluminum. These substituted compounds have a composition which may be represented by the general formula Al.sub.1-x Ga.sub.x As, wherein x has values of between 0.3 and 0.4. It has generally not been possible, however, to prepare stable semiconductor crystals having this formula wherein x has values of less than 0.3, i.e., wherein the gallium arsenide content is less than 30 mole percent.
We have now found that aluminum arsenide crystals, wherein gallium has been substituted for a minor portion of aluminum, i.e. less than 30% of the aluminum, can be prepared which have improved chemical stability.
It is therefore an object of the present invention to provide a method for the preparation of crystals of aluminum arsenide, wherein gallium has been substituted for a minor portion of the aluminum, which have improved chemical stability.
It is another object of the present invention to provide a method for the preparation of pseudo-binary crystals of aluminum gallium arsenide which contain 30 mole percent or less gallium arsenide and which are stable under ambient conditions.
It is still another object to stabilize aluminum gallium arsenide semiconductor crystals, which contain 30 mole percent or less gallium arsenide.
These and other objects of the invention and the manner in which they can be attained will become apparent from the following detailed description of the method of the invention.